Phone test set modem

ABSTRACT

A phone test set provides modem capability in a hand held device, enabling bi-directional data communications. Demodulation is provided by sampling digitized incoming phone line signals at 4 times carrier frequency, and employing values representing 0 and 90 degree samples to extract the information signal.

BACKGROUND OF THE INVENTION

This invention relates to test and measurement data communications andmore particularly to a phone test set modem apparatus and method.

Communications field service technicians in the telephone industry use atest instrument called a phone test set or lineman's handset. The phonetest set typically comprises ear and mouthpieces and keyboard fordialing input. Some models include alphanumeric displays.

The test set is used by the technician in the installation andtroubleshooting of analog phone systems. FIG. 1 is a view of acontemporary phone test set 10 which is a hand held device comprising aninput keypad 12 and alphanumeric display 14. Microphone 16 and speaker18 enable the technician to speak and listen to use the device as atelephone. Cables 20 connect alligator clips 22, 24 and modular plug 26to the test set to enable connection to telephone wiring of the phonesystems under test. The test set typically will include features such ascaller ID and call waiting caller ID. What has been missing from phonetest sets is the capability for bi-directional alphanumeric datacommunication between the test set and other devices connected to thephone line.

SUMMARY OF THE INVENTION

In accordance with the invention, a phone test set is provided withmodem functionality to enable digital communication between the test setand other devices connected remotely through the phone lines.

Accordingly, it is an object of the present disclosure to provide animproved phone test set with digital communication capability.

It is a further object of the present disclosure to provide an improvedphone test set apparatus providing bi-directional alphanumeric datacommunication in addition to telephone capabilities.

The subject matter of the present invention is particularly pointed outand distinctly claimed in the concluding portion of this specification.However, both the organization and method of operation, together withfurther advantages and objects thereof, may best be understood byreference to the following description taken in connection withaccompanying drawings wherein like reference characters refer to likeelements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a contemporary phone test set

FIG. 2 is a block diagram of a phone test set in accordance with thepresent disclosure;

FIG. 3 is a block diagram of a demodulation device for FSK signals;

FIG. 4 is a block diagram of implementation of the demodulation in thepresent device;

FIG. 5 is a diagram illustrating an example digitized signal input tothe low pass filter;

FIG. 6 is a diagram illustrating an example signal output from the LowPass Filter; and

FIG. 7 is a diagram illustrating an example signal output from thethreshold decision block.

DETAILED DESCRIPTION

The system according to a preferred embodiment of the present disclosurecomprises a phone test set system and method providing modemcapabilities to enable the test set as a bi-directional alphanumericdata communication terminal.

FIG. 2 is a block diagram of a phone test set in accordance with thepresent disclosures. The test set 30 employs a processor 32 interfacingwith keypad 12′, display 14′, microphone 16′, speaker 18′ and interfacecables 20′ for connection to a phone network. Power block 34 providesoperational power to the device, and may comprise battery power, or linepower, for example. Within the processor, an implementation is providedof a modulator/demodulator to interface with the phone line forreceiving input signals for demodulation, and with the processor forproviding demodulated data to the processor. Also, the processormodulator implementation supplies data for transmission back to thephone line 20′. Alternatively, in a particular embodiment, the modulatormay be separate from the processor.

FIG. 3 is a block diagram illustrating a demodulation device for FSKsignals, wherein input, from phone line 20′ is provided to an FMdiscriminator 36. The discriminator if implemented in hardware comprisesa phase splitter (capacitors 38, 40, inductor 42 and resistor 44) andmultiplier 46, to receive the original signal and phase shifted signal(90 degrees) and the output thereof is supplied to Low Pass Filter 48.The output from Low Pass Filter 48 is supplied to a threshold decisionblock 50, which determines whether the signal represents a one or zero,depending on the level value of the signal. The resulting output fromblock 50 is a binary data pattern of ones and zeros, which is suppliedto processor 32 which implements a universal synchronous/asynchronousreceiver/transmitter (USART). The incoming signal suitably representsand ASCII data stream, so the processor USART decodes the data providingthe character stream data as input to suitable software for reading thedata. The data may comprise caller ID information or, more importantly,any data stream such as text or command/control data for communicatingbetween the test set and a remote device over the phone line, such asanother test set or a test instrument at a remote location.

Tayloe discusses an analog product detector, in U.S. Pat. No. 6,230,000,wherein an input analog signal is passed through a commutating switchwith 4 outputs, each output being connected for successive 90 degreeportions of the frequency of the input signal, supplied to detectingcapacitors. Each of the 4 capacitors provides baseband product detectionvalues at 0, 90, 180 and 270 degrees of the input. The 0 and 90 degreeoutputs multiplied provide the original information signal.

The above FM discriminator can be implemented algorithmically with adigital system. Referring to FIG. 4, a block diagram of theimplementation, in a preferred embodiment, incoming signals from phoneline 20 are sampled at 4 times the carrier rate by A to D converter 52.The signals are suitably FSK signals in a particular embodiment,comprising 1200 and 2200 Hz, and sampling of the incoming signals isdone at 6800 Hz (assuming a carrier frequency of 1700 Hz being theaverage of the 2 frequencies (1200+2200)/2)). Sampling at four times thecarrier frequency provides sufficient data to create the FMdiscriminator mathematically. FIG. 5 illustrates an example sampledsignal output from A to D converter 52. Synthetic discriminator 54receives the 4 times carrier rate sample data, and a current sampledatum from the A to D is multiplied by a previous sample datum from theA to D, which represents the sample 90 degrees prior to the currentsample, providing the output function of an FM discriminator bymultiplying the 0 and 90 degree signal samples, for example. The outputof discriminator 54 is passed through a Low Pass Filter 56, a 5 poleButterWorth LPF in the particular embodiment, an example of the filteredoutput being illustrated in FIG. 6. The LPF output is then supplied to athreshold detector 58, which determines whether the value represents aone or zero data bit and that output is suitably provided to theprocessor which implements a USART, for decoding of ASCII datatherefrom. FIG. 7 illustrates example resulting output data of thethreshold detection.

For transmission of data from the test set to the phone line, amodulator is provided to FSK encode data as supplied by the processor totransmit the same on the phone line.

In a particular embodiment, an anti-aliasing low pass filter (suitably 4kHz) is provided at the input of the A to D converter to remove noiseabove the telephone speech band. The processor can comprise, forexample, a Microchip Corporation PIC24FJ128GA110 microcontroller, orother processor with analog to digital converter, USART and baud rateclock generator capability.

The A to D, sampling, algorithmic FM discrimination, low pass filteringand USART functions can all be implemented by operation of theprocessor.

The A to D sampling of the phone line signals is made and the resultingsamples are employed to an FM discriminator function that employs the 90degree out of phase signals to compute the demodulated data value. Thatresulting value is supplied to a programmed low pass filter, and theoutput of the filter is supplied to a threshold detection function,which provides the zero and one data output to the USART input, fordecoding of ASCII data (for example).

Accordingly data communication reception of FSK signals is provided tothe phone test set, as well as transmission of the same, enabling thephone test set to operate as a digital smart terminal or to transmit orreceive commands and control remotely.

While a preferred embodiment of the present invention has been shown anddescribed, it will be apparent to those skilled in the art that manychanges and modifications may be made without departing from theinvention in its broader aspects. The appended claims are thereforeintended to cover all such changes and modifications as fall within thetrue spirit and scope of the invention.

1. A phone test set comprising: an A to D converter for receivingincoming phone line signals and providing digitized output of theincoming phone line signals sampled at four times a desired frequency;and a discriminator receiving said digitized output and multiplying onesof said samples together to extract a signal of interest from saidincoming phone line signals.
 2. The phone test set according to claim 1,wherein said phone test set comprises a hand held ‘butt set’.
 3. Thephone test set according to claim 1, further comprising a thresholddetector receiving said extracted signal of interest and providing abinary output representation of said extracted signal of interest. 4.The phone test set according to claim 1, further comprising a low passfilter receiving said signal of interest from said discriminator toprovide a low pass filtered version thereof.
 5. The phone test setaccording to claim 4, further comprising a threshold detector receivingsaid low pass filtered version of said signal and providing a binaryoutput representation of the input thereto.
 6. The phone test setaccording to claim 5, further comprising a universalsynchronous/asynchronous receiver/transmitter receiving said binaryoutput representation and providing an ASCII value output representedthereby.
 7. The phone test set according to claim 3, further comprisinga universal synchronous/asynchronous receiver/transmitter receiving saidbinary output representation and providing an ASCII value outputrepresented thereby.
 8. The phone test set according to claim 1, whereinsaid digitizing is at approximately 6800 Hz.
 9. The phone test setaccording to claim 1 wherein said signals of interest are 1200 and 2200Hz.
 10. A method of providing a phone test set with a modem to extractinformation modulated onto a signal on a phone line, comprising: A to Dconverting an input signal to the phone test set to provide digitizedsamples of the signal on the phone line to the phone test set; providingsaid digitized samples selected at four times a carrier frequency ofinterest; and multiplying ones of said digitized samples representing 90degree out of phase samples to extract said information modulated ontothe signal.
 11. The method according to claim 10, further comprisingthreshold detecting said extracted signal of interest and providing abinary output representation of said extracted signal of interest. 12.The method according to claim 10, further comprising a low passfiltering said signal of interest from said discriminator to provide alow pass filtered version thereof.
 13. The method according to claim 12,further comprising threshold detecting said low pass filtered version ofsaid signal and providing a binary output representation of the inputthereto.
 14. The method according to claim 13, further comprisingproviding a universal synchronous/asynchronous receiver/transmitterreceiving said binary output representation and providing an ASCII valueoutput represented thereby.
 15. The method according to claim 11,further comprising providing a universal synchronous/asynchronousreceiver/transmitter receiving said binary output representation andproviding an ASCII value output represented thereby.
 16. The methodaccording to claim 10, wherein said carrier frequency is approximately1700 Hz.
 17. The method according to claim 10, wherein said informationcomprises signals at 1200 and 2200 Hz.
 18. A hand held phone test setcomprising: an A to D converter for receiving incoming signals on aphone line and providing digitized output of the incoming phone linesignals sampled at four times a desired frequency; and a processorreceiving said digitized output and implementing a discriminator,multiplying ones of said samples together to extract a signal ofinterest from said incoming phone line signals, said processor furtherimplementing a threshold detector receiving said extracted signal ofinterest and providing a binary output representation of said extractedsignal of interest, said processor further implementing a universalsynchronous/asynchronous receiver/transmitter receiving said binaryoutput representation and providing an ASCII value output representedthereby.
 19. The hand held phone test set according to claim 18, furthercomprising a modulator for modulating data and transmitting outgoingsignals on the phone line.
 20. The phone test set according to claim 18,wherein said sampling is at approximately four times a carrier frequencyof a sampled baseband signal.